1. Field of the Invention
The present invention relates to a thermal transfer image receiving sheet to be used in a state superimposed with a thermal transfer sheet.
2. Description of the Related Art
As a method for forming an image utilizing the thermal transfer, a method for forming a full color image with a thermal transfer sheet having a sublimation dye as a recording material supported by the surface of a base material sheet made of a paper, a plastic film or the like and a thermal transfer image receiving sheet provided with a receiving layer of a sublimation dye on the surface of a paper or a plastic sheet superimposed, is known. According to the method, since the sublimation dye is used as the color material, the density gradation can be adjusted freely so that the original full color image can be expressed on the image receiving sheet. Since the image formed by the dye is extremely vivid and has the excellent transparency, the excellent reproductivity of an intermediate color or the gradation can be provided so that a high-quality image coming up to the silver salt photograph can be formed.
In order to form a high-quality printed image on an image receiving sheet at a high speed by a sublimation type thermal transfer method printer, a dye receiving layer containing a dye dyeing property resin (a resin having a property to be easily dyed by a dye) as the main component on the base material or the image receiving sheet. When a paper material such as a coat paper and an art paper is used as a the base material of the image receiving sheet, since the thermal conductivity of these materials is relatively high, the dye receiving sensitivity in the receiving layer becomes lower.
Then, as it is disclosed in Japanese Patent Application Laid Open (JP-A) No. 5-16539, a biaxial oriented foamed film having a gap inside, containing a thermoplastic resin such as a polyolefin as the main component can be used as the base material for the image receiving sheet. Since an image receiving sheet using such film as the base material has an even thickness, the flexibility and a smaller thermal conductivity compared with a paper made of a cellulose fiber or the like, it is advantageous in that an even image with a high density can be obtained. However, in the case a biaxial oriented film is used for the base material of the image receiving sheet, the residual stress at the time of drawing is alleviated by the heat at the time of printing so that the film is contracted in the drawing direction. As a result, curling and wrinkles are generated in the image receiving sheet so that a trouble such as paper jam or the like may be generated at the time of running the image receiving sheet in a printer.
In order to improve the disadvantage, as it is disclosed in JP-A No. 3-268998, there is an example of using a laminated sheet as the base material of the image receiving sheet, the laminated sheet is manufactured by attaching and laminating a biaxial oriented foamed film having a gap on a core material having a relatively small thermal contraction ratio or a core material having a large elastic modulus.
Moreover, there is also a thermal transfer image receiving sheet manufactured by superimposing a non foamed plastic film on a core material via an adhesive including a foaming agent and foaming the foaming agent in the state to make the adhesive layer be a porous structure (see JP-A No. 6-23040). A technique of forming a porous layer having both the insulation property and the cushion property by coating a porous layer coating solution made of hollow particles mixed in a binder resin onto a base material sheet is known (see JP-A No. 2002-212890).